1. Field of the Invention
The present invention relates to a golf club shaft and a golf club using this golf club shaft.
2. Description of the Prior Art
Golf club shafts (hereinafter also referred to simply as “shafts”) made of FRP (fiber reinforced plastics) are known in the art. The FRP shaft is formed into a tapered shaft by winding a plurality of prepregs, which are made of carbon fiber impregnated with uncured thermosetting resin, on a mandrel in the shape of a tapered shaft and thermally curing the plurality of prepregs wound on the mandrel. Although such a plurality of prepregs are conventionally used as a combination mainly of the following different types prepregs: a UD (unidirectional) prepreg(s) (prepreg whose unwoven fibers are all bundled and extended in a single direction), a straight layer(s) whose long fibers are parallel to the longitudinal direction of the shaft, a bias layer(s) whose long fibers are angled relative to the longitudinal direction of the shaft at a predetermined angle, and a hoop layer(s) whose long fibers are angled relative to the longitudinal direction of the shaft at an angle of 90 degrees, shafts including prepregs made of woven fabric composites have become more common in recent years.
The assignee of the present invention has proposed a shaft including a tetra-axis woven fabric prepreg (see Japanese Unexamined Patent Publication No. 2000-245880) and another shaft including a biaxial woven fabric prepreg (plain weave fabric prepreg) and a triaxial woven fabric prepreg (see Japanese Unexamined Patent Publication No. 2006-61473) as shafts that include prepregs made of woven fabric composites.
However, in the shafts disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 2000-245880 and 2006-61473, no consideration has been made from the viewpoint of the vibration damping performance of the shaft. “Vibration damping performance” is one of the indicators showing the ability to damp (attenuate) vibrations of the shaft. Specifically, the higher the vibration damping performance, the less vibrations caused when the club head impacts a golf ball are transmitted to the player, and the lower the vibration damping performance, the easier vibrations caused when the club head impacts a golf ball are transmitted to the player. If the golf player continues to use the shaft whose vibration damping performance is low for years, the burden on the golf player's body increases, which could be a cause of injury to the golf player. Therefore, the vibration damping performance is an important factor which may improve or deteriorate the performance of the shaft. However, not much research and development having its main focus on the vibration damping performance thereof have been carried out on shafts in the past. Specifically, not much research and development that pay attention to the effect on the shaft vibration damping performance due to lamination of textile materials have been carried out on shafts.
On the other hand, due to the tendency toward weight reduction of the shaft in recent years, although the weight of woven fabric prepregs exerts an influence on the sense of use to the golf player at a level of several to over ten grams (per unit of area) and imposes restrictions on shaft design, a biaxial woven fabric prepreg is high in density due to the structure thereof, thus unavoidably becoming at least approximately 170 grams per square meters (300 grams per square meters in the case of a heavy biaxial woven fabric prepreg). Namely, using a biaxial woven fabric prepreg in itself in a similar manner to the shaft disclosed in Japanese Unexamined Patent Publication No. 2006-61473 has given rise to less design flexibility from the viewpoint of the weight of the shaft using woven fabric prepregs.
In short, in conventional shafts, there have been certain limits to development of a shaft having both a high vibration damping performance and design flexibility from the viewpoint of the shaft weight in line with the stream of weight reduction.